Sets whether the menu item appears justified at the right side of a menu
bar. This was traditionally done for "Help" menu items, but is now
considered a bad idea. (If the widget layout is reversed for a right-to-left
language like Hebrew or Arabic, right-justified-menu-items appear at the
left.)

Set the accelerator path on the menu item, through which runtime changes of
the menu item's accelerator caused by the user can be identified and saved
to persistant storage (see accelMapSave on this). To setup a default
accelerator for this menu item, call accelMapAddEntry with the same accel
path. See also accelMapAddEntry on the specifics of accelerator paths, and
menuSetAccelPath for a more convenient variant of this function.

This function is basically a convenience wrapper that handles calling
widgetSetAccelPath with the appropriate accelerator group for the menu
item.

Note that you do need to set an accelerator on the parent menu with
menuSetAccelGroup for this to work.